In petroleum refining, there is large-scale use of catalysts in the hydroprocessing of hydrocarbon feeds to remove contaminants, such as sulphur-containing compounds, nitrogen-containing compounds, and, optionally, contaminant metals, such as nickel, vanadium, and iron. Apart from removing contaminants, hydroprocessing may also effect some hydrocracking of the feedstock to compounds with a lower boiling point. The catalysts used in these processes are well-known in the art. They generally consist of a Group VI hydrogenation metal component, e.g., molybdenum or tungsten, and a Group VIII hydrogenation metal component, e.g., cobalt or nickel, on a refractory oxide carrier. The oxidic support generally consists of alumina, optionally mixed with other components, such as silica, silica-alumina, magnesia, titania or mixtures thereof. The catalyst may additionally comprise other components, such as phosphorus.
During the hydroprocessing of hydrocarbon feeds, the activity of the catalyst decreases. This is caused, int. al., by the accumulation on the catalyst surface of carbonaceous and sulphurous deposits, which are generally referred to as coke. The accumulation of these deposits is detrimental to the activity of the catalyst. Therefore, a coked-up catalyst is commonly regenerated after a certain period of use by burning off the coke, which renders the catalyst suitable for reuse. However, this process of use and regeneration by coke removal cannot be kept up indefinitely. This is because during the use of the catalyst other, irreversible, processes also take place which detrimentally affect the catalyst's activity. For example, the dispersion of the hydrogenation metals through the catalyst composition decreases during use, which leads to a catalyst with decreased activity. Further, if the catalyst is used for the hydroprocessing of feedstocks containing contaminant metals such as vanadium, nickel, and iron, contaminant metal deposits will form upon the catalyst. Additionally, during catalyst use, the particle strength and the length of the particles decreases. Thus, in the life of each hydroprocessing catalyst there comes a time when regeneration by coke removal is not sufficient to regain a catalyst with sufficient catalytic activity, and the catalyst must be replaced. The so-called spent hydroprocessing catalyst then has to be disposed of.
One way of disposing of spent hydroprocessing catalyst is by landfilling, but this is becoming increasingly difficult because of environmental constraints. Catalysts used for the hydroprocessing of metals-containing hydrocarbon feeds, which will thus contain contaminant metals such as vanadium, nickel, and iron in addition to the hydrogenation metals, may be disposed of to a metals reclaimer, who will reclaim not only the hydrogenation metals but also the contaminant metals. Obviously, metals reclaimers are primarily interested in spent catalysts containing substantial amounts of contaminant metals, and far less so in catalysts which have been used for the hydroprocessing of lighter feedstocks and so contain no or hardly any contaminant metals. This means that it is even more difficult to dispose of spent hydroprocessing catalysts used for hydroprocessing lighter feedstocks than of hydroprocessing catalysts used for hydroprocessing heavy feedstocks. In any case, both landfilling and metals reclaiming are expensive.
Another option which has been considered in the art is the reuse of spent catalyst to form new catalyst compositions. Such a process is known from U.S. Pat. No. 4,888,316, in the name of Phillips Petroleum Company. In this reference a process is described in which a substantially dry spent hydroprocessing catalyst comprising hydrogenation metals, a support material, and coke is ground. The ground product is mixed with an alumina-containing binder, after which the mixture is shaped. The shaped particles are subsequently subjected to a temperature treatment to remove the coke from the catalyst composition. In a specific embodiment, the decoked particles are subsequently subjected to a high-temperature calcination step which is carried out in such a manner that the resulting catalyst composition has a larger portion of pores in the 5-60 nm range than the product obtained after the removal of carbonaceous deposits. Said high-temperature calcination step is preferably carried out at a temperature of 593-927.degree. C. (1100-1700.degree. F.). The drawback to the process described in this reference is that it requires facilities for handling coke-containing catalyst dust not present in a normal hydroprocessing manufacturing plant. It also requires additional precautions in respect of health, safety and environmental (HSE) hazards. Further, it was found that the catalyst obtained by the process described in this reference does not show adequate strength for it to be used in a commercial process, nor is the homogeneity of the catalyst sufficient.
The purpose of the present invention is to provide a process for preparing a large-pore hydroprocessing catalyst from spent hydroprocessing catalyst by which a catalyst is obtained which does show adequate strength and homogeneous quality, and which can be produced without the need for additional equipment or HSE measures for handling coke-containing catalyst dust.